Conventionally, when flowing an alternate pulse current through an inductance load such as an induction coil for an induction heating device, it is necessary to apply a high voltage from the power supply to change the current, due to the effect of magnetic (snubber) energy stored at the inductance load.
In order to flow the alternate pulse current through the induction coil by a conventional voltage-type inverter comprising semiconductor switches, the inverter must generate voltage corresponding to changes in the electric current. A difference in phase is brought about between the current and the voltage of the inverter, and the power supply becomes a so-called power supply with a low power factor.
It is possible to improve the power factor by connecting a resonance capacitor, which is often used in high frequency circuits, to the induction coil in series or in parallel, and it is, thereby, possible to reduce the inverter capacity. However, it was only possible for the inverter, for the induction heating device, using a fixed resonance capacitor to improve the power factor thereof only at a frequency specified by L and C.
By using the Magnetic Energy Recovery Switches (hereinafter, “MERSes”, see Patent Literature 1), which store magnetic energy of the circuit and supply the energy to the load, and by turning ON/OFF them, the voltage necessary for changing the current drastically can be generated automatically by the current coming into a magnetic energy storage capacitor, thereby making it unnecessary for the power supply to provide the voltage.
FIG. 2 shows an alternate pulse current generating device already suggested by the inventors of the present invention. (see Patent Literatures 2 and 3.)
As shown in FIG. 2, when MERSes are inserted between AC power supply 5 and inductive load 3 and turned ON/OFF in synchronization with the AC power supply 5, magnetic energy of the inductive load 3 is stored in energy storage capacitor 2 and the energy is recovered (regenerated) again by the inductive load 3; therefore transient voltage generated by the inductance of the inductive load 3 is all generated by the MERSes.
In case that alternate pulse current is flown through an inductive load having mainly inductance component and a little resistance, it was necessary, conventionally, to apply a high voltage, from the power supply, corresponding to changes in the electric current, by the effect of magnetic energy stored at the inductive load. However in the case shown in FIG. 2, there is a merit that the necessary apply voltage is only the voltage corresponding to the resistance (a low electric voltage). In view of this merit, the patent application was filed.    [Patent Literature 1] Japanese Patent Publication No. 2000-358359    [Patent Literature 2] Japanese Patent Publication No. 2004-260991    [Patent Literature 3] Japanese Patent Publication No. 2005-223867